The metal lithium of thin film batteries reacts rapidly upon exposure to atmospheric elements such as oxygen, nitrogen, carbon dioxide and water vapor. Thus, the lithium anode of a thin film battery will react in an undesirable manner upon exposure to such elements if the anode is not suitably protected. Other components of a thin film battery, such as a lithium electrolyte and cathode films, also require protection from exposure to air, although these components are commonly not as reactive as thin metal anode films. It should therefore be desirable to incorporate within a lithium or lithium intercalation compound battery, which includes an anode of lithium and other air-reactive components, a packaging system that satisfactorily protects the battery components from exposure to air.
Polymer batteries have been constructed in a manner in which the battery has a porous anode and cathode. The partially constructed battery cell is then placed within a protective “bag” which is sealed along three edges. Once the battery cell is positioned within the bag a liquid electrolyte is injected into the bag to occupy the space within the porous spacer between the anode and cathode. The open edge or forth edge of the bag is then heat sealed, as shown in U.S. Pat. No. 6,187,472. During the last steps of this process however air or other gases occupy spaces within the bag. These gases are entrapped within the bag once it is sealed. Much care must also be exercised during the sealing process to insure that the heat seal does not contact the battery cell within the bag as the heat will harm the polymer battery cell.
In the past packaging systems for batteries have been devised which included a shield which overlays the active components of the battery. These shields have been made of a ceramic material, a metallic material, and a combination of ceramic and metallic materials. The construction of thin film batteries however have proven to be quite difficult to produce and in providing an appropriate barrier as gas pockets may be capture between the anode and the protective layer during construction.
Another thin film battery packaging system has been devised wherein alternating layers of parylene and titanium are laid over the active components. The alternating layers are provided to restrict the continuation of pin holes formed in the layers during construction. This method of producing a protective layer has been difficult to achieve and has provided a protective layer which remains effective for only a short time.
It thus is seen that a need remains for a packaging system for thin film batteries which overcomes problems associated with those of the prior art. Accordingly, it is to the provision of such that the present invention is primarily directed.